There is a growing need for a carrier or operator to independently evaluate various next generation wireless technologies in order to assess, at an early stage in the development, the impact of specific implementation features on performance. A simulation platform provides the ability to progressively design and test proprietary components leading to a system solution. Its intelligent use can save R&D dollars by reducing design problems before the building of prototypes and actual products. In addition, it enables the early and forward communication of the advantages of an innovation and its implementation. The ability to demonstrate early can provide significant market advantage when inviting business from potential clients. Such simulation platforms are often built from a combination of commercially available and internal developments and the methods of usage need to be tuned to the internal development processes and the product development objectives. Because of this heterogeneity, importance is attached not only on the development but also to the methods of usage within the development process of an organization as the development progresses from concept to reality.
In the context of a digital cellular communications system, such as cdma2000, each data bit is modulated and transmitted with a unique high rate code known to the receiving system, this modulation entailing the bandwidth of operation to be expanded or “spread”. Codes are mathematical in origin and great importance is attached to the discovery of codes that are “orthogonal” to each other. Orthogonality refers to the exclusiveness of a code. Data which are spread by many different orthogonal codes can, however, be transmitted simultaneously, enabling savings in system resources, and demodulated uniquely at the different receivers. During a call made on a digital cellular system there are numerous exchanges of data, signalling and pilot message transmissions between the base station and the mobile. Different kinds of message transmissions may contain different codes, spreading rates, modulations and signal strengths. Each of these consumes system resources and the goal of an efficient network is to minimize use of system resources while offering competitive performance to its users. Newer standards, such as cdma2000, provide greater flexibility of operation, tighter control, and higher complexity algorithms and signal processing in the quest for better quality of service. This increases the importance of methods and apparatus for early verification of the system.
A simulation platform would need to provide multiple cell environments with various mobility and Quality of Service (QoS) needs, provide visibility of cross-layer interactions, compare the result of changes in features and parameters and output impact on performance, display results and statistical distributions, and support simultaneous forward (base station to mobile) and reverse (mobile to base station) link simulations. When higher granularity is needed on particular areas in the simulation, the simulator must have provision to include other commercial or proprietary lower link level modules and simulations.
Although numerous simulator developments exist, there is a lack of cohesion between the development and the methods of usage within the development process. There is, in particular, no formal or known approach or methodology regarding the use of such commercially-available simulators to assess the dynamically changing quality of operation of a cellular network depending on the channel conditions and on user traffic. Neither is there formal methodology for deploying a market-critical Push-to-Talk/VoIP application.
By way of reference, OPNET Technologies, Inc. based in Bethesda, Md. develops and markets a generic simulation toolkit under the registered trademark OPNET™ which requires significant innovation, tuning and characterization in order to be made useful for any particular application. The OPNET™ simulation toolkit is basically an event driven simulation engine. An event is a request for a particular activity to occur at a particular point in time. Time, in the simulation, advances when the event occurs. The simulation engine maintains a single global event list and all objects access a shared simulation time clock. Events are scheduled on the list in chronological order and an event may have data associated with it. An event is removed from the list when it has been processed. Some events may have to be initialized on the list. An event list is dynamic as events are always being added and deleted from the list. An event is pending until it is executed and pending events can be cancelled. Simulation time advances only when an event with a later time is taken from the list. No simulation clock advance occurs during an invocation of a process model nor does it advance during transition between states. There are two kinds of states in which the basic finite state machine on which processes are modelled may reside. Forced states are those in which a process invokes the ‘enter’ and then the ‘exit’ executives, evaluates the condition statements associated with transitions and if exactly one condition evaluates to true, then that transition is executed. Unforced states are those in which the process invokes the enter executive and stops after this. It then releases control to the simulation kernel and becomes idle, resuming at the suspension point and executing the exit executives when next invoked and followed by executing a transition based on the condition that is true. A process model must be in an unforced state for time to advance. These fundamental software-oriented characteristics require a level of abstraction between the real-life system to be simulated and the simulation platform. As such, there is need in the art for a radio access simulator for evaluating signal processing and control.